Currently, concepts of green riding and low-carbon life have been increasingly accepted and implemented by society. With the development of the times and the emphasis on healthy living, the bike is no longer only a means of transportation anymore, and bicycle riding has become a new form of exercise that has entered into our lives.
Existing bicycles usually use chain transmission structures, which essentially includes a crank, a wheel disk, a bicycle chain, a freewheel, etc. Namely, the wheel disk is driven to rotate by treading the pedals, and then the bicycle chain connected between the wheel disk and the freewheel is driven by the wheel disk, and the freewheel mounted on the rear wheel is driven to rotate by the bicycle chain, such that the rear wheel is driven to rotate and the bike thus moves forward. The chain transmission structure is simple with low manufacturing cost. However, a phenomenon of disengagement of the bicycle chain (namely, the disengagement of the bicycle chain from the wheel disk and the freewheel) occasionally occurs. In addition, since the bicycle chain is exposed the elements, as time goes by, the bicycle chain rusts easily such that the service life of the bicycle is reduced, thus this structure needs to be further improved.